IB Biology 5.2 Natural Selection Notes

Introduction

Natural selection is a fundamental concept in biology that describes the process by which certain traits become more common in a population due to the survival and reproductive advantages they confer. This mechanism, first articulated by Charles Darwin, is the driving force behind evolution and the diversity of life on Earth. In this study note, we will delve into the details of natural selection, its mechanisms, and examples that illustrate its principles.

Key Concepts of Natural Selection

Overproduction of Offspring

Most species produce more offspring than can survive to adulthood. This phenomenon, known as overproduction, ensures that there is a large pool of individuals competing for limited resources.

• Example: A single oak tree can produce thousands of acorns each year, but only a few will grow into mature trees.

Variation

Within any population, there is variation among individuals. This variation is due to differences in genes (genetic diversity), mutations, and sexual reproduction.

• Example: In a population of beetles, some may be green while others are brown. This color variation can affect their survival depending on the environment.

Competition

Because resources such as food, shelter, and mates are limited, individuals must compete for them. This competition acts as a selection pressure that influences which individuals survive and reproduce.

• Example: In a drought, only plants with deeper root systems may survive due to their ability to access water from deeper soil layers.

Differential Survival and Reproduction

Individuals with traits that provide a survival or reproductive advantage are more likely to survive and reproduce. These advantageous traits are then passed on to the next generation at a higher frequency.

• Example: In a population of rabbits, those with thicker fur may be more likely to survive in cold climates, leading to more offspring with thick fur in subsequent generations.

Inheritance

The traits that confer a survival advantage must be heritable, meaning they can be passed from parents to offspring through genes.

• Example: The ability of some bacteria to resist antibiotics is due to genetic mutations that can be inherited by subsequent generations.